Notes 12

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Notes 12 Chemical Reactions

• Sci 10 Chemistry

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A chemical reaction

• A chemical reaction takes place when one or more
  substances change to form new substances a
  chemical change
• A chemical reaction is identified by the presence
  of one or more signs

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Signs of Chemical Change

1. An energy change
2. An odour change
3. A colour change
4. Formation of a gas (i.e. bubbles produced)
5. Formation of a precipitate (a solid) in solution

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Signs of Chemical Change

• All chemical change implies a change in energy
• The Law of the Conservation of Energy energy can
  be transferred (change in type of energy) but the
  quantity (amount) of energy stays the same during
  a reaction
• Examples of types of energy temperature change
  (thermal energy), light production, sound
  production, electrical energy

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Endothermic vs. Exothermic

• Exothermic reaction energy is released
• i.e. an explosion
• There is always a release of energy when bonds
  are formed
• i.e 2H2(g) O2(g) ? 2H2O (l) thermal energy
• Energy on the products side exothermic reaction
• Endothermic reaction energy must be added before
  the reaction can start
• i.e. cooking an egg (energy added thermal
  energy/heat)
• Energy is always needed to break chemical bonds
• i.e. thermal energy 2H2O (l) ? 2H2(g) O2(g)
• Energy on the reactants side endothermic
  reaction

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To Do

• p.185 4, 5
• p.189 3, 4
• p.202 4
• Notes 11 Practice 2